Although it varies from brand to brand, the majority of laxatives lose their effectiveness within 24 hours. According to numerous HealthTap contributors, the majority lose effectiveness within eight hours.
According to WebMD, mineral oil and other lubricant laxatives facilitate rapid excretion, whereas fiber-based laxatives and stool softeners place less stress on the body and may take up to a week to reach full effectiveness. Milk of Magnesia and other osmotic laxatives pull water from the colon and necessitate many glasses of fluids to reach their full effectiveness. Ex-Lax and other stimulant laxatives may cause rapid defecation, but long-term use might develop to dependence.
